Treatment of metals



Patented June 25 1929.

UNITED STATES PATENT OFFICE.

FLOYD C. KELLEY, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

TREATMENT OF METALS.

No Drawing.

My invention relates to the treatment of metals to prevent harmfuldeterloratlon when heated to high temperatures 1n the presence ofoxygen.

metal andform therewith a surface alloy' which serves to protect theinterior of the foundation metal. This surface alloy of chromium and thefoundation metal is fundamentally a protection against corrosion,although it also resists oxidation at high temperatures to some extent.

I have discovered that if the article to be protected be suitably heatedin surface con-.

tact With a mixture of powdered chromium and silicon, a surface alloy isformed with I the metal of the article which has excellent oxidationresisting properties when heated to high temperatures. Variousproportions of silicon may be used. Preferably the powdered chromium-andsilicon are mixed with a powdered iiiert, refractory material, such asaluminum, oxid or magnesium oxid. I have found that if 10 per cent byweight of powdered silicon be added to the regular chromium mixture ofmy aforesaid patentconsisting of equal-parts of powdered chr0- mium andrefractory material, either aluminum oxid or magnesium oxid, anexcellent heat resisting surface alloy may be formed. The articles to betreated are packed in a receptacle in the chromium silicon treatingmixture and then suitably heated, for example, by placing the receptaclewith its contents in' a hydrogen furnace. z 1 The duration of the heattreatment or firing to efi'ect'thefldesired penetration of the chromiumand silicon with the" foundation metal Varies. with the temperatureused; Temperatures offrom 1000 k to 1500 C. are satisfactory. While a teperature of approximately 12OQ C. is required to elfec t penetration ofthe powdered chromium alone, when thifsismall amount of powdered siliconis addedto' the treating mixture good penepreciably,

Letters Patent of the Application filed April 17, 1925. Serial No.23,970.

tration is obtained at approximately 1000 C. Apparently the siliconalloys with the chromium and carries the chromium with it into thefoundation metal at this lower temperature. When iron is bein treated, avery satisfactory surface alloy is formed by firing for six hours at atemperature of 1350 C. As with the process described in my aforesaidpatent, the firing is carried out under non-oxidizing conditions,preferably in the presence of hydrogen.

The surface alloy thus formed gives excellent protectionagainstgoxidation at surprisingly high temperatures. A piece of ironafter being given the treatment previously described, i. e. fired forsix hours at a temperature of 1350 C., was heated at a temperature of1100 C. in an open furnace for over 200 hours before any signs ofbreakdown in the protective coating Were perceived. Another piece ofiron after being given a similar treatment was heated in the open air ata temperature of 900 C. for over 400 hpurs without showing anyappreciable oxidation. This latter piece showed only an exceedinglysmall increase in Weight after being thus heated, which is afurtherindication of the efficiency of this surface alloy as a protectivecoating. 1 I

f the firing temperature is reduced apfor example, to approximately 900C. but little, if any, further penetration of the chromium siliconmixture takes place, and the surface alloy whenv subjected totemperatures of 90OC. or less remains fixed.

.In other words, there is little orno tend ency at this or lowertemperatures for the chromium and silicon of the surface alloy togradually diffuse into the interior of the foundation metal and therebyleave the surface unprotected. This is probably one explanation of theextraordinary heatresisting properties obtained by this treatment.

What I claim as new and desire to secure by United States, is, 1. Themethod of protecting metals against oxidation at: high emperatures whichconsists in heating the metal at a temperature of from 1000 C. to 150OC. in a hydrogen atmosphere in contact with a mixture of powderedchromium and silicon.

2. The method ofprotecting metals against oxidation at high temperatureswhich consists in heating the metal under non-oxidizing conditions at atemperature of from 1000 C. to 1500 C. in contact with a mixture ofpowdered chromium and silicon.

3. The methodvof providing iron with a heat protecting surface alloy ofiron, chromium and silicon which consists inheating the iron in hydrogenin contact with a mixture of powdered chromium, silicon and alu- 'minumoxid at a temperature of from 1000 10 C. to 1500 0.

surface alloy which is resistant to oxidation at high temperatures,which consists in heat-' ing the iron in hydrogen in contact withpowdered chromium and silicon at a temperature of approximately 1350 C.

In witness whereof, I have hereunto set my hand this 16th day of April,1925.

FLOYD C. KELLEY.

